Coatings applied to surfaces typically serve decorative and/or protective functions. This is particularly so for automotive finishes, which must provide an esthetically appealing appearance while simultaneously meeting and maintaining rigorous performance and durability requirements. As used herein, "automotive coating or finish" encompasses both original equipment (OEM) coatings and refinish coatings, but especially to refinish coatings, the later term referring to coatings which are applied after the car has left the manufacturer, usually for repair purposes. It will be appreciated that refinish coatings often have different application and performance parameters.
Pigments are used in coatings to provide decorative and/or protective functions. As used herein, "pigment" refers to a fine, insoluble white, black, or colored material, typically suspended in a vehicle for use in a paint or ink. The term "pigment" may also include effect pigments such as micas, metallic pigments such as aluminum, opalescent pigments, and the like.
Dry pigments comprise a mixture of primary particles, aggregates, and agglomerates that must be wetted and de-aggregated before dispersion forces can take full effect and enable the production of a stable, pigmentary dispersion in the medium of choice. Aggregates, or primary pigment particles joined face-to-face, must be reduced to their fundamental primary particle. An ideal dispersion consists of a homogeneous suspension of primary particles. See Organic Pigments, Federation Series on Coatings Technology, 2.sup.nd Edition, Lewis, P. October 1988, Revised March 1995, pgs. 39-41, hereby incorporated by reference.
Although pigments are acknowledged as a required component in many coatings, their presence may be a possible contributing factor to a variety of problems in liquid coatings and/or dry paint films. Examples of coatings/paint film defects thought to be attributable to pigments include: undesirable gloss due to aggregates, blooming, pigment fading, pigment flocculation and/or settlement, separation of pigment mixtures, `pigment shock` in millbases, instability in pigment suspensions, brittleness, moisture susceptibility, fungal growth susceptibility, and/or thermal instability. See Physical-Chemical Aspects of Pigment Applications, Surface Coating Reviews, Guthrie, James T., and Lin, Long, Oil & Colour Chemists' Association, 1994, Sections 4.3.1-4.3.2, hereby incorporated by reference.
It has been recognized that the level of dispersion in a particular pigment containing coating composition affects the application properties of the wet composition as well as the optical properties of the cured film. Improvements in dispersion have been shown to result in improvements in gloss, color strength, brightness, and gloss retention. Dispersion--the neglected parameter. JOCCA, W. Carr, 65, 373 (1982).
The prior art has long sought improved pigment dispersions for use in coating compositions, particularly with respect to pigments that are difficult to disperse such as carbon black and transparent oxides.
The use of cellulose esters in organic solvent borne coatings has been known to impart desired properties such as improved pigment dispersions, improved metallic flake orientation, improved solvent release, and higher gloss coatings. They are also known to function as rheology control agents in solvent borne coating formulations.
U.S. Pat. No. 3,959,193 discloses a combination of an aryl sulfonamide-formaldehyde resin and film forming material, such as cellulose acetate butyrate, which may further include a surfactant, such as a non-ionic surfactant including, for example, an alkylarylpolyether, as a "universal" dispersant for resin additives, such as pigment materials. The composition generally includes 40 to 90 weight percent of any of various types of additives, including pigments.
U.S. Pat. No. 5,521,304 provides water soluble or water dispersible cellulose acetoacetate esters prepared by contacting a cellulose material with diketene, an alkyl acetoacetate, 2,2,6-trimethyl-4H-1,3-dioxin-4-one or a mixture thereof and a carboxylic anhydride in a solvent system comprising lithium chloride plus a carboxamide. Compositions containing the cellulose acetoacetate esters are disclosed to be useful for coating applications.
Amine-containing cellulose esters, eg, the acetate N,N-diethylaminoacetate and propionate morpholinobutyrate have been suggested for use in controlled-release, rumen-protected feed supplements for ruminants. Such esters are prepared by the addition of the appropriate amine to the cellulose acylate crotonate ester or by replacement of the chlorine on cellulose acylate chloroacetate esters with amines. However, such amine containing cellulosic materials are not taught to be useful in coating compositions nor do they suggest the particular compositions of the invention. They lack an enamine structure, hydroxyl groups and the use of mixed acetate/butyrate esters.
Eastman Chemical Products, Inc's Publication No. X-263A, December, 1986, pgs. 2-3, discusses the possible reactions of acetoacetylated polymers. The carbonyl group of the acetoacetylated polymers is said to chelate with metals such as zinc, tin, lead, aluminum, copper and zirconium. Polyvalent cations are taught to useful for crosslinking purposes. In addition, the preparation of enamines by the reaction of amines with carbonyl groups is taught. Diamines are shown to crosslink acetoacetylated polymers.
Despite these prior art attempts, there still exists a need for improved pigment dispersion, especially with respect to the dispersion of certain pigments intended for use in topcoat finishes. Topcoat finishes require a high quality of color depth and richness, especially with pigments such as carbon black and the like. Such high quality of color depth and richness, known as "jetness" with respect to carbon black, has been difficult to obtain in an efficient and cost effective manner with prior art dispersants and dispersion processes. "Jetness" as used herein refers to a clean looking color with blue undertones.
Accordingly, it is desirable to obtain an improved dispersion with respect to pigmented coating compositions. It is further desirable to obtain such improved dispersion with an agent that is economical and easily obtained. More particularly, it is desirable to obtain a dispersant for use with pigments, especially hard to disperse pigments such as carbon black, which would provide coatings having an improved appearance, especially as to color and/or jetness, when pigments dispersed with such a dispersant are incorporated into the coating.